I just put more live rock into my tank and now my clown is staying in the top corner breathing hard, should I be worried or is this just caused by fear and it will fade?
No, unless there is enough die-off on the rock to cause another spike. If you have an established tank, then you should buy fully-cured LR. OR, you can buy cheaper, not so cured LR and cure it yourself in a seperate garbage bin or something.
Hmm...I'd be hesitant about accepting the LFS' word on "Oh, yes, this rock is FULLY cured..." Seems to me it'd be a good idea to put it in a tub for a couple days to monitor die-off.